Presently, when an integrated circuit (IC) chip receives a clock signal which is higher than the normal clock rate, the chip may generate unpredictable results due to variations in voltage, temperature, and process manufacturing. For this reason, a high frequency monitor is generally implemented in most IC designs. The high frequency monitor is used to turn off the clock signal to an IC chip when the frequency exceeds a predetermined value which may cause the IC chip to generate unpredictable results.
Presently, most high frequency monitors are comprised of two basic components: a ring oscillator and a clock comparison circuit. The ring oscillator is used to provide a know reference frequency. The clock comparison circuit is used to compare the reference clock signal from the ring oscillator to that of the clock signal being sent to the IC chip and to ensure that the clock signal to the IC chip is within the bounds of the reference clock signal.
While current high frequency monitors which use a ring oscillator and a clock comparison circuit do work, they have several problems associated with them. The main problem with high frequency monitors which use a ring oscillator is that they are very inaccurate. These systems have a variance of two (2) times the clock variance. These inaccuracies place a limit on how close a clock signal may come to the detection frequency of the IC chip. Another problem with these types of high frequency monitor circuits is that they consume large amounts of power which may decrease the efficiency of the system using the high frequency monitor circuit. A further problem with high frequency monitors which use a ring oscillator is that these systems require the use of a set frequency. Once the ring oscillator is set in silicon, the frequency of the ring oscillator cannot be altered. Thus, even if the IC chip is able to run at different frequencies, a high frequency monitor which use a ring oscillator cannot be altered to monitor the different operating frequencies of the IC chip.
Therefore, a need existed to provide an improved over frequency detection circuit. The improved over frequency detection circuit must be more accurate than current high frequency monitors which use a ring oscillator and a comparison circuit. The improved over frequency detection circuit must further provide a low power way to ensure that IC chips do not generate unpredictable results at a frequency higher than the normal clock rate. The improved over frequency detection circuit must be dynamic. The improved over frequency detection circuit must allow an IC chip to run at the chip's maximum attainable frequency, while requiring no advance knowledge of the maximum chip frequency.